The top-ranked high school prospect in the class of 2012, Lucas Giolito, left last night's start with one out in the seventh inning.

It was initially reported by the Los Angeles Times that Giolito had sustained a groin injury. Perfect Game contacted Giolito's father, Rick, to confirm details of the situation.

Perfect Game has learned that Lucas felt a pull in the elbow after delivering a pitch during the seventh inning of last night's game. He was immediately removed and underwent range of motion tests with Harvard-Westlake's medical staff and felt no pain.

This morning Giolito underwent an MRI at the Kerlan-Jobe Orthopaedic Clinic in Los Angeles. The MRI revealed a very slight sprain in the ulnar collateral ligament (UCL), no surgery is required.

The recovery plan calls for Giolito to begin a rehab program immediately. He will not throw at all for four to six weeks, after which time he will be re-evaluated. Once he is cleared to begin throwing again he will begin a throwing program.

Contrary to previous reports, the timetable for his full recovery is unknown at this time. While everyone will be cautious with his recovery, it is not out of the question that he could be able to return to the mound before the end of the CIF Southern Section playoffs, which conclude on June 2.

Giolito ranks No. 1 in Perfect Game's 2012 MLB Draft Top 500 Prospects which were released in January, and has widely been speculated to be on the short list of candidates to be selected first overall by the Houston Astros on June 4.

The UCLA commit is expected to make a full recovery with no long-term effects.